A promising statistical approach for studying the collisional excitation induced by CO: Application to the CS–CO system

Abstract

The calculations of rate coefficients for the interpretation of molecular spectra are a recognized computationally expensive task. This is particularly true for media like comets, where the dominant species (CO, CO2, and H2O) have relatively high masses. Currently, no clear methodology exists to treat the collisional excitation of heavy species at low temperatures, thus limiting the number of collisional studies on such species. We present here a promising statistical approach to determine collisional rate coefficients of heavy systems as an alternative to fully quantum calculations when heavy projectiles such as CO are considered. This is illustrated through the determination of the first rate coefficients for the collisional excitation of CS induced by CO of cometary interest. The CS–CO rate coefficients were computed up to 30 K, and the accuracy of the data was assessed by comparison with rate coefficients computed using the fully quantum time-independent close-coupling approach restricted to the minimal partial wave J = 0. The excellent agreement between the two sets of data demonstrates that the proposed method can be both fast and reliable to study the collisional excitation of molecules induced by CO at low temperatures.